Chism, then 14, followed the young educator into a school bathroom and attacked her, raping, strangling and stabbing her at least 16 times before stuffing her body into a garbage can, officials have said.

He brought her into the nearby woods where prosecutors said he assaulted her with a tree branch and left her body with a note that read "I hate you all." He was acquitted of that rape charge.

He was also convicted of armed robbery for stealing Ritzer's credit cards and her underwear.

Judge David Lowy pronounced the sentence on Friday after hearing victim impact statements from Ritzer's loved ones, who described a young woman who always positive and was passionate about her work, the Associated Press reported.

"Colleen Ritzer lived a life of quiet heroism. The crashing waves of this tragedy will never wane," Lowy said, calling her death "brutal and senseless."

Prosecutors had asked that Chism stay in prison for at least 50 years, while his attorney Susan Oker asked that her client receive a sentence that would make him eligible for parole by the time he was 40.

She cited studies that said a juvenile brain is not fully developed.

Chism's mother, Diane Chism, released a statement expressing her condolences to Ritzer's family.

"Words can't express the amount of pain and sorry these past 2 1/2 years have been," she said. "However, there is no one who has suffered more than the Ritzer family. My utmost esteem, prayers and humble respect is with them today as they continue their journey to heal."